There has so far been known a belt type transmission apparatus as a vehicular continuously variable transmission (hereinafter simply referred to as a “CVT”). The belt type transmission apparatus comprises a drive side pulley and a driven side pulley respectively serving as movable sheaves, and an endless power transmission belt passing over the drive side pulley and the driven side pulley. The power transmission belt to be used for such a CVT is constituted by an endless band-like ring serving as a core material, and a multiplicity of elements each having a thickness in the axial direction of the endless band-like ring and retained by the endless band-like ring. The elements are subject to being pressed toward the axial direction of the endless band-like ring, and serve to impart tensions to the endless band-like ring, thereby allowing a torque to be transmitted from the drive side pulley to the driven side pulley.
As one typical example of power transmission belt, there have so far been used many power transmission belts each of which comprises a multiplicity of elements each formed with a pair of left and right concave portions open toward both sides of the element in the width direction of the power transmission belt, and a pair of endless band-like rings respectively received in the concave portions to ensure that the multiplicity of elements are held between the pair of endless band-like rings. In this kind of the power transmission belt, each of the elements has one surface side formed with a rocking edge so that the neighboring elements can relatively be rocked in the state that the plurality of elements are held in contact with the preceding elements by the rocking edges intervening therebetween when the transmission belt is wound on each of the pulleys. In order to efficiently produce the elements of the power transmission belt such as those previously mentioned, there has so far been known (see, for example, Patent Document 1) a method of efficiently producing the elements through the steps of preparing a steel plate in a band-like form (hereinafter simply referred to as a roughly formed material) subjected to a roll work so that stepped portions having different thicknesses are formed between a central portion and end portions in the width direction thereof, and sequentially punching the elements from the roughly formed material at the position where the stepped portion comes to the rocking edge.
In the case that each of the elements thus produced is deemed to be disqualified in flatness level, both of neighboring stacked elements cannot be brought into tight contact with each other, thereby making it difficult to have the elements assembled with the rings and further leading to uneven gaps each formed between the neighboring stacked elements. This results in decreased power transmission efficiency between the drive side pulley and the driven side pulley by the power transmission belt. In view of this problem, there has so far been known a method of producing the elements through a step of determining whether or not each of the elements is disqualified in flatness level with distortion and bending thereon by determining if there is a change more than a predetermined contraction amount in the overall length of the stacked elements when different inspection loads of large and small are applied to the elements in a stacked condition. (see, for example, Patent Document 2).